Cipher apparatus



Jan. 13, 194 M. c. MOM. OBRIEN CIPHER AFPARATUS Filed May 11, 1939 e Sheets-Sheet 1 Jan. 13, 1942. M. c. MOM. O'BRIEN 2I270I137 CIPHER APPARATUS v Filed May 11, 1939 es Sheets-Sheet s Jan. 13, 1942.

M. C. M M. OBRIEN CIPHER APPARATUS Filed May 11, 1959 6 Sheets-Sheet 4 Jan. 13, 1942- M. c. McM. O'BRIEN CIPHER APPARATUS Filed May 11, 1959 6 Sheets-Sheet 5 fmw Jan. 13, 194;. M. c. MCM. OBRIEN 7 2,270,137-

CIPHER APPARATUS Filed May 11, 1959 6 Sheets-Sheet 6 Patented Jan. 13, 1942 2,270,137 c rnnn APPARATUS Morgan Cyprian England, assignor to McMahon OB ien, Baldock, Brien Cipher Machines Limited, London, England, a British company Application May 11, 1939, Serial No. 273,120

. In Great Britain June 27, 1938 11 Claims.

This invention relates to apparatus, for en ciphering and deciphering messages, of the kind comprising a plurality of individually movable elements arranged side by side, each carrying a cipher alphabet and each movable to a plurality of diiierent positions corresponding to the letters of a plain alphabet. When all the elements have been moved the enciphered or deciphered message is read from the cipher alphabets, a suitable reading line being provided for this purpose.

The term alphabet is herein used to mean the letters of the alphabet and/or the digits and/or any other symbols or characters. The term letter is herein used to mean any character in such an alphabet. The term plain alphabet means the alphabet arranged in a normal order while the term cipher alphabet means the alphabet arranged in any arbitrary order.

According to one aspect of the present invention, an enciphering and deciphering machine of the kind described comprises a plurality of flexible endless bands arranged side by side and settable individually each to any one of a number of positions corresponding to alphabet and carrying each a pair of reciprocal cipher alphabets arranged side by side lengthwise of the band, and means providing a reading line common to all the cipher alphabets.

The pair of alphabets on each band are preferably. printed in different colours, for example, one in black and the other in red, and, for convenience, one will be referred to as the black alphabet and the other as the red alphabet.

With the present arrangement a message can be enciphered by setting the bands in accordance with the letters of the message and reading either the black letters or the red letters at the reading line. The cipher message can be deciphered by setting the bands in accordance with the letters of the cipher message and reading the black letters if the message was enciphered by means of the red letters or vice versa. The

machine provides thus two alternative ciphers each of which can be used to encipher a message or to decipher a message enciphered by means of the other.

By the term reciprocal alphabets is meant two cipher alphabets such that a letter enciphered by means of one alphabet can be decipheredby enciphering the cipher letter by means of the other alphabet.

To facilitate reading the black or the red letters at the reading line, in enciphering and deciphering, there may be provided a comb arranged to the letters of a plain cover the black letters only or the red letters only at the reading line and movable transversely of the bands so that either the red letters or the black letters may be visible.

According to another aspect of the present inband will lie on a straight lap of the band, and

a plurality of means each providing a reading line to a dififerent one of the cipher alphabets on each band.

' After setting the bands, a reading can be taken at any of the reading lines so that a message can be enciphered in any of two or more ciphers without any adjustment being made to the machine.

According to another aspect of the present invention an enciphering and deciphering machine comprises a plurality of steel or like strong tapes supported side by side, each carrying a plain alphabet and formed with a perforation or projection adjacent each letter of the plain alphabet, a member extending across all the tapes and forming a stop to limit the movement of a stylus or the equivalent engaged with a perforation or projection on one of the tapes, and two spaced hooks or clips carried by each tape in positions to. engage opposite ends of a paper or like strip and hold the paper 'or lik strip on the tape.

With this arrangement the cipher alphabet or alphabets is printed on the paper or like strip so that the cipher can be changed by replacing each strip by another. Further the tape itself can be'of steel or'other strong material so that it willwithstand rough usage due to its being set, while the strip can be of paper, fabric or other Weak material which is cheaper than the material of the tape. Thus, changing the cipher merely involves changing the relatively inexpensive strips and does not involve the changing of the more expensive tapes.

When the strips are made of paper, one of the hooks or clips is preferably movable relatively to its tape and is spring-pressed in a direction to maintain the strip in tension. When the strip is made of fabric, it may be provided with at one of its ends so that it the line 9-4; of Figure 1,

will be tensioned between the hooks or clips on its tapes.

The present invention also provides a paper sheet cut to form a plurality of strips connected together at each end by upper and lower marginal portions, perforated to form a tear-line between each marginal portion and the adjacent end of each strip and provided with holes one at each end of each strip. Each strip carries one or more cipher alphabets. The sheet is placed on the tapes of the machine just described and the holes on the strips are engaged with the hooks on the tapes. portions are then torn off leaving each strip properly supported on its tape.

Specific embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a plan view of one form machine,

Figure 2'. is a section on the line 22 of Figure 1,

Figure 3 is a plan view of the central part of the machine showing some of the tapes inthe positions they occupy when a message has been enciphered,

Figure 4 is an underplan illustrating the manner in which the second series of cipher alphabets are read,

Figure 5 shows a suitable form of paper sheet for use with the apparatus,

Figure 6 is an enlarged sectional view showing the spring-plungers for tensioning the paper strips,

Figure 7 is a view corresponding to Figure 6 but showing the plunger in the position it occupies when tension is relieved for replacing the paper strips,

Figure 8 is a section, to the line 8--8 of Figure 1,

Figure 9 is a section, to an of the ephr an enlarged scale, on

enlarged scale, on

Figure 10 is an elevation of the spring-cover,

Figure 11 is a perspective view of the complete machine in its operating position,

Figure 12 is a detail of a modification to the strip, and

Figure 13 shows an alternative able pulleys.

As shown in Figures 1 to 10 the machine comform or replace- 3 prises two side-plates Ill, ll of synthetic resin or other suitable light material interconnected by cross-bars l2, 13, by axles l4, l5 and other crossmembers described below. Each axle supports a number of pulleys l6 which are independently rotatable on the axles.

The cross-bars I2 and I3 support upper and lower grooved plates I], 88 of synthetic resin which serve to support the tapes hereinafter described.

Passing around each aligned pair of pulleys I 6 is a strong steel endless tape l9a, l9b, etc., each of which tapes, as shown in Figures 1 and'lO, is printed with what is herein termed a plain alphabet; that is to say, the twenty-six letters of the alphabet in their normal order followed by the ten numerals in their normal order. Adjacent each of these thirty-six characters is a hole for engagement by the point of a stylus, pencil or other tool whereby the steel tape may be moved endwise of its length. As shown in Figures 1 and 2 each tape carries near the beginning of the plain alphabet a metal plate 2| formed with a lug-portion 22, the purpose of which is explained hereinafter, and a hook-portion 23 -for engaging The upper and lower marginal a hole in the end of a paper strip 24. At a point in its lower lap, as seen in Figure 2, each steel tape also carries a bracket 25, the two arms of which form a support for a plunger the details of which are seen in Figures 6 and 7. The plunger comprises a rod 26 carrying a flange or collar 21 which is engaged by a spring 28 the other end of which abuts against the right-hand limb of the bracket 25. The right-hand end of the plunger is turned over to form a hook 29 which passes through a slot 30 in the steel tape IS. The lower plate I8 is formed with a plurality of grooves 3| each of which accommodates the plunger-bracket 25as shown in Figures 6, '7 and 9'. The spring 28 ordinarily maintains the paper-strip 24 in tension as shown in Figure 6. The manner in which this tension is automatically relieved will be explained. below with reference to the operation of the machine.

Referring to Figures 1 and 2, it will be seen that the side-plates I0 and H are additionally braced by means of a cross-bar 32 which also constitutes a rearward abutment for a fiat metal plate 33 which is slidable in grooves 34, 35, in the sideplates l0 and II respectively. The metal plate 33 has an upstanding front ledge 84 for engagement by the fingers of an operator and for co-operating with the lugs 22 of the plates 2|. It also carries a wire releasing shaft having a central handleportion as shown, journal-portions 36 to engage with bearings 37 formed on the plate 33, and teeth 38 Which project down through holes in the plate (Figure 9) to co-operate, in a manner hereinafter described, with depressions 39, 40 formed in the marginal portions of the top plate IT. The teeth 38 are continuously pressed downwardly by springs '10 each of which is anchored at one end to the wire shaft 85 and at the other end is turned over as shown at 1| to rest on the plate 33.

The machine so far described is covered as to part of its upper surface and substantially the whole of its lower surface by means of the spring cover shown in Figure 10. This comprises a long lower limb 4| which lies underneath the machine with its left-hand end resting on a metal plate 42 (Figure 2) secured to the side-plates I0 and H, and a short upper limb 43 which overlies the right-hand end of the upper surface of the machine. The cover is located against endwise movement by downward protuberances 44 which engage co-operating depressions in the sideplates l 0 and I I; the resiliency of the cover causes these protuberances to snap into position when the cover is pushed home. The cover is located against lateral movement by engaging rebates 45, 46, (Figures 8 and 9) formed in the sideplates I0, II, respectively. At the end of its shorter and upper limb the cover 43 carries a sliding channel-shaped plate 41 by means of studs 48 on the'plate which engage elongated holes 49 in the cover. The plate 4! carries forwardly-projecting comb-like wire teeth 50 which co-operate with the characters of the cipher alphabets on the paper strips in a manner described below. The plate 47 also carries an upwardly-projecting pin 5| which passes through an elongated hole 52 in the cover whereby the plate may be shifted from one position in which the teeth 50 obscure the characters in the righthand cipher alphabets to another position in which they obscure the'characters in the lefthand cipher alphabets. The cover is also formed witha hole 53 and the bottom of the plate 41 beneath this hole is suitably coloured, for example, by black and red spots, so that the position to which the comb has been. moved may beseenv at a glance by inspecting the colour visible through the hole 53. A

As shown in Figure 4, the cover 43 is formed on its underside with a rectangular readingaperture 54 through which the characters on the paper tapes are visible. Adjacent the aperture 54 the cover carries a channelled plate 55 (Figure similar to the plate 41', having comb-like teeth 56 similar to the teeth projecting into a position in which they are visible through the aperture 54 when the machine is turned upsidedown. The plate has an operating pin 51 and may be mounted in the same manner as the plate 41. The cover may be similarlyformed with a hole like the hole 53 for the purpose of indicating at a glance the position to which the comb has been moved.

Each of the paper strips 24 carries four cipher alphabets, each of thirty-six characters, in two pairs. When the steel tapes are in their initial or zero positions, as shown in Figure 11, the first pair of alphabets extends from a point just beyond the teeth 59, around the pulleys on the axle IE, to a point in advance of the reading aperture 54. The second pair extends from just beyond the aperture 55 to a point near the hooks 29. Each pair of cipher alphabets comprises two sets of characters which, though arbitrarily arranged, are related each to the other in such manner that if a character dialled on the steel tape gives a certain cipher character on one set, that cipher character dialled on the steel tape will give the original character on the other set. For example, if the steel tape 19a is moved until the letter C lies adjacent the edge of the metal plate 33, the character 7 appears adjacent the first comb-tooth 59 as shown in Figure 3; if the comb is now moved to its other position by means of the pin 5!, and the steel tape 1911 moved to a position in which the character '7 lies adjacent the edge of the plate 33, the letter C will appear adjacent the tooth 5! The two sets of characters in the second pair of cipher alphabets are reciprocal in like manner.

The two pairs of cipher alphabets are spaced apart endwise of the paper strips so as to leave a gap of the height of one character. Such a gap is shown as 86 in Figure 12. Thus, when the steel tapes are in their zero positions, none of the cipher-characters is visible on any of the paper strips, either at the comb 5G or the aperture 54.

It will be understood that the cipher alphabets are normally diiierent for each paper strip.

Remaining details of construction of the machine will appear from the description, which now follows, of the manner in which the machine is operated.

The machine is laid on a table or other suitable support with its left-hand end (referring to Figure 1) towards the operator and itsrighthand end away from him. Let it be assumed that the message to be enciphered begins with the word Chicago. The operator first decides which of the ciphers he is going to use, that is to say, whether he will use the cipher alphabets extending from the comb 53 to the comb 56 or the cipher alphabets extending from the comb- 56 to the plungers 25. Assuming that the first of these ciphers is to be used, he sets the comb 50 in the appropriate position for enciphering by operating the pin 5 l. Forexample, the arrangement may be such that, for enciphering, thehole 53 shows thecolour: black and the wire teeth Ell! obscure the right-hand column. of letters on the paper stripsand, for deciphering, the hole 53 shows the colour red and the teeth 50 obscure the left-hand characters. As shown in Figure 11, the operator first inserts the point of a. stylus or pencil into the hole 20 in the steel tape i9a; opposite the letter C and. draws the pencil towards him until its movement is arrested eitherby the forward edge: of the plate 33 or, preferably, by the forward edge of a fixed reading plate 60 shown in Figures 1 and 2. During this movement the point of the stylus or pencil is accommodated beneath the steel tape by a groove 6l'a, formed in the upper plate I! (Figure 8') a similar groove filb, 51c etc. being provided beneath each of the other tapes 19b, 190 etc. During the operation of drawing the stylus towards him, the operator directs his attention to the next steel tape I91) and looks for the letter H so that he neednot look at thefirst tape [9c again. When the movement of the first tape is arrested by the plate 6!] he removes the stylus and inserts it in the hole opposite the letter H in the second tape I911. The first seven tapes are thus all moved until they occupy the positions shown in Figure 3. The remaining tapes are, of course, moved according to the remaining thirteen of the first twenty letters of the message but the present description deals, for the sake of simplicity, with only the first seven letters. When all thetwenty tapes, as shown, have been moved in this way the plain-language message will have been set up along the edge of the reading plate $11 as shown in Figure 3. By reading along this line the operator can immediately detect and correct any errors of operation which may have occurred.

The operator now reads the cipher letters between the teeth 50, that is to say, the twenty letters, the first seven of which are 7VV85FX. This cryptogram is written down and the steel tapes are nowall returned to their initial neutral positions by pressing forwardly on the ledge 84 of the sliding plate 33. The forward edge of this plate engages during its travel with the lugs 22 of the plates 2| whereby all the steel tapes are restored. Movement of the sliding plate 33 is limited, however, by the automatic engagement of the teeth 38 with the foremost depressions 39 in the top plate IT. The plate 33 is now returned to the position shown in Figures 1 and 11 its return movement being limited by the crossbar 32, and the next twenty characters of the message are enciphered and checked, and the cryptogram written down as before. The operation of the machine continues in this way until the entire message has been enciphered.

It will now be supposed that a correspondent, having an exactly similar machine with exactly similar paper strips, receives the cryptogram and wishes to decipher it. He proceeds in exactly the same way and, to make this clear, reference will be made to the first seven letters of the received message. The deciphering operation is performed with the comb 50 in the position in which it obscures the left-hand end cipher charactors and exposes the right-hand end characters. With the parts in the position shown in Figure 11, the operator takes his stylus, inserts the point in the hole 20 adjacent the character 7 in the steel tape |9a and slides the steel tape along until the movement of the stylus is arrested by the reading bar 60'. He then proceeds to setup the characters- VV85FX on the succeeding six tapes until the cryptogram appears along the reading bar 60 where it can be checked with the received message. When the tapes are set up in the manner above described, the message will appear between the teeth 50, beginning with the word Chicago.

As has already been explained each paper strip 24 carries two pairs of cipher alphabets end to end, the alphabets of each pair being reciprocal alphabets as above defined. Thus the machine contains two complete ranges of cipher for each set of paper strips used. It is intended that the range of cipher shall be changed at frequent intervals and one change can be made by using the cryptogram appearing at the aperture '54 instead of that appearing between the teeth 50. For example, instead of transmitting the cryptogram 7VV85FX the first operator could have sent the cryptogram LOEPGAN. This message, when received, would have been deciphered by shifting the plate 55 into its other position, moving the steel tapes according to the cryptogram, and reading the plain-language message at the aperture 54.

However, the paper strips may be completely renewed in a simple manner as follows. The spring-cover 43 is removed by means of a suitable knob !2. The metal plate 33 is now slid forwardly until the teeth 38 engage the notches 39. At this point the steel tapes are all in their neutral positions as has been explained above. The operator now lifts the handle-portion 85 of the wire-shaft whereby the teeth 38 become disengaged from the notches 39 and further forward movement is possible. The plate 33 is pressed forwardly whereby all the lugs 22 of the plates .2l are pressed to the right as shown in Figure 2. However, the plungers 26 are incapable of moving further to the left because of their engagement with the ends 73 of the grooves 3| in the bottom plate l8, so that the result of such additional movement is to compress the springs 28 whereby all the plungers 26 move into the position illustrated in Figure 7. Tension on the paper strips is thus relieved whereby the strips can readily be removed from the hooks 23 and 29 and destroyed. i

The simplest manner of replacing the strips is to use a sheet of paper as shown in Figure in which the individual strips 24 are connected together at each end by lateral strips 14. The sheet thus formed is provided with perforations forming tear lines at the junction of each strip M with the strips 24. The entire sheet is placed in position on the machine by engaging the holes 16 with the hooks 23, wrapping the sheet around the pulleys of the axle l5 and engaging the holes 1'! with the spring-pressed hooks 29 on the underside of the machine. The sliding plate 33 is now withdrawn to the position in which the teeth 38 engage the first notches 39 thus the sheet of paper is tensioned by the springs 28. The two strips 14 are now torn oif and the strips 24 are thus'independent of one another and individually movable. The metal cover, 43 is now replaced and the machine is ready for use.

In an alternative form of the invention, the strips of paper may be stored separately and suitably numbered so that they may be applied separately and in the proper order to the steeltapes. I

- While it is desirable that the cipher alphabets should be readily replaceable in the manner above referred to where great secrecy is necessary, it is possible to obtain a useful cipher of less secrecy by printing the cipher alphabets on the steel tapes in the manner of the plain alphabets. It will be understood that, with such an arrangement, it is necessary to renew the steel tapes I 9 in order to change the cipher range.

In the third possibility, the removable strips, instead of being of paper, may be of fabric as shown in Figure 12. The strip 24 is formed with eyelets 18 one at each end for engagement by the hooks on the steel tape. It is possible to dispense with the plunger-mechanism of Figures 6 and '7 by providing each strip 24 with an elastic portion 19 to facilitate its application to and removal from the steel tape. By the use of fabric strips as shown in Figure 12 the same strips can be used for a long period, or can be brought back into use after having been temporarily discarded.

The pulleys 16 are preferably of light metal such as aluminium alloy and, according to a preferred form of the invention, may be separated from one another by steel washers 80 as shown in Figure 13. The steel washers serve the purpose of locating the pulleys in their correct position along the axles i4 and I5 and also of locating the steel tapes I 9.

The spring-cover shown in Figure 10 has the advantage that it enables th strips bearing the cipher alphabets to be readily replaced. No threading of the strips beneath reading lines or other obstructions is necessary as it would be if the combs 50 and 56 were fixedly carried by the side-plates l9 and II. Moreover, the underpart 4| of the cover protects the strips bearing the cipher alphabets during operation of the machine so that, if the machine is resting upon an uneven surface, the paper strips are free to move without risk of being torn.

It will be seen that the complete machine is of very small overall dimensions, the exact size depending on the necessary size of the individual characters used on the metal tapes and the paper strips and upon the number of steel tapes required. In the example described with reference to the drawings, the machine has twenty steel tapes, each carrying a paper strip and this number, where the cipher range is changed from time to time, is found to give a cipher of great subtlety. However, it would be possible in some circumstances to use a smaller number of tapes and it might be advisable, in other circumstances, to use a larger number. It will be understood that there is no limit to the number of tapes which could be employed and, Where it is not necessary for the machine to be readily portable, a very much larger number would be used.

It will be seen that, for all operative positions of the steel tapes, the character to be dialled lies on a straight lap of the steel tape and the corresponding characters of the cipher alphabets also lie on a straight lap. By this arrangement the selection of the appropriate hole 29 for the insertion of the stylus, and the reading of the cipher characters, is greatly facilitated.

In the machine above described the alphabets on the paper strips are reciprocal alphabets in order that the same machine and same paper strips may be used both for enciphering a message and deciphering the resulting cryptogram. In an alternative form of the invention, however, the cipher alphabets need not be reciprocal alphabets but a different machine would then have to be used for deciphering from the machine used for enciphering.

Enciphering and deciphering can be performed very rapidly with a machine according to the invention. In one method of working, two or more machines may be used the paper strips of which may be identical or, preferably, different so as to increase the subtlety of the cipher. Two operators are employed. Number one takes the first machine, enciphers the message, and checks the cryptogram. He hands this machine to number two who types the cryptogram and transmits it; meanwhile number one proceeds to encipher the next batch of letters by means of the second machine. A similar procedure may be adopted for deciphering.

I claim:

1. An enciphering and deciphering machine comprising a plurality of flexible bands arranged ide by side and settable individually each to any one of a number of positions equal to the number of characters in a plain alphabet and allocated respectively and consecutively to said characters, n

said bands carrying each a pair of reciprocal cipher alphabets arranged side by side lengthwise of the band.

2. An enciphering and deciphering machine comprising two spaced axles, a plurality of pulleys rotatable on each axle, a plurality of tapes each supported by one of the pulleys on each axle and carrying a plain alphabet and a plurality of different cipher alphabets arranged endto-end lengthwise of the tape, a plate extending across said tapes whereof the edgeconstitutes a reading line common to all the plain alphabets which reading line is spaced from one of the pulleys at a distance greater than the length of tape occupied by the plain alphabet so that, be-

fore a tape is set, the plain alphabet on that tape will lie on a straight lap of the tape, a cover extending across said tapes and a plurality of apertures therein constituting a reading line to each different one of the cipher alphabets.

3. Apparatus of the kind described comprises two spaced axles, a plurality of pulleys rotatable on each axle, a plurality of tapes each supported by two of said pulleys, one on each axle, each tape carrying a plain alphabet and a plurality of different cipher alphabets arranged end-to-end lengthwise of the tapes.

4. An enciphering and deciphering machine comprising a plurality of steel or like strong tapes supported side by side, each movable in the direction of its length, each carrying a plain alphabet and each formed with a perforation or projection adjacent each character of the plain alphabet, a member extending across all the tapes and forming a stop to limit the movement of a stylus engaged with a perforation or projection on one of the tapes, and'two spaced hooks carried by each tape to engage opposite ends of a paper or like strip and hold the said strip on the tape.

5. Enciphering and deciphering apparatus comprising a plurality of endless bands supported side by side, each carrying a plain alphabet and formed with perforations adjacent the characters of the said alphabet, a member extending across the bands to limit the movement of an implement engaged with one of said perforations, two spaced hooks carried by each tape to engage opposite ends of a paper strip, and means for spring-pressing one or both of said hooks in such direction as to maintain said paper strips in tension.

6. Cipher apparatus comprising aplurality of endless bands arranged side by side, two hooks carried by each band to support a strip of paper between them, a plunger carrying one of said hooks and spring-pressed in a direction to tension the paper strip, a frame-member constituting an abutment for said plunger whereby movement of the band beyond a limiting position relieves said tension whereby the paper strip may be removed and replaced.

7. In a cipher apparatus, an endless metal tape, hooks spaced apart lengthwise of the tape to support a paper strip between them and means acting upon one hook to press it resiliently away from the other and so maintain the paper strip in tension.

8. Cipher apparatus comprising a plurality of strips arranged side by side and individually and successively movable in accordance with the characters of a message to be enciphered or of a cryptogram to be deciphered, a pair of reciprocal cipher alphabets side by side on each strip one on the right-hand side and the other on the left-hand side thereof, and an adjustable comb having a series of teeth adapted to obscure wholly or partly either the right-hand cipher characters of all the strips or the left-hand characters, in a certain reading position, according to the position of adjustment of the comb.

9. Apparatus for enciphering and deciphering messages comprising a pair of spaced axles, sideplates carrying the ends of said axles, a plurality of pulleys on each axle, a plurality of endless metal bands each passing around two pulleys, one on each axle, a plurality of apertures in each band, a stylus engageable with said apertures for selectively driving the bands around the axles,

means for mechanically arresting movement of the stylus and therefore of the band with which it engages, a plurality of lugs, one on each band, a sliding plate engaging said side-plates and adapted to engage with all of said lugs to return the bands all to a zero position, and means to limit the returning movement of said bands.

10. Apparatus as claimed in claim 9, wherein said limiting means comprises a notch in each side-plate and a pair of spring-pressed teeth carried by the sliding plate and adapted to engage with said notches.

11. Apparatus as claimed in claim 9 comprising, in addition, two spaced hooks for engaging and supporting a strip of less robust material, one said hook being carried on the same straight lap of the band as that against which the said arresting means lies, and the second hook being carried on the other straight lap, a plunger associated with the said second hook, a spring normally operative to press the said plunger, and therefore the said second hook, in a direction to maintain said strip in tension, a fixed abutment for cooperation with said plunger, a notch in each said side-plate, a pair of spring-pressed teeth carried by the sliding plate and adapted to engage with said notches when the bands are returned to their zero positions by engagement of said sliding plate with said lugs, a second pair of notches in said side-plates, and means for releasing said teeth from the first said notches whereby the sliding plate may be pressed into a position in which the teeth engage the second notches, the plungers are all arrested by their engagement with the abutments and the distance between the two hooks on each band is thus reduced, for the purpose of renewing the-said strips.

MORGAN CYPRIAN MCMAHON OBRIEN. 

